Usually, when they talk about the size of the Universe, they mean local fragment of the Universe (Universe)which is available to our observation.
This is the so-called observable Universe - the region of space visible to us from Earth.
And since the age of the universe is about 13.8 billion years, no matter which direction we look, we see light that reached us in 13.8 billion years.
So, based on this, it is logical to think that the observable Universe should be 13.8 x 2 \u003d 27.6 billion light years across.
But this is not the case! Because over time, space expands. And those distant objects that emitted light 13.8 billion years ago have flown even further during this time. Today they are more than 46.5 billion light years away. Doubling that equals 93 billion light years.
Thus, the real diameter of the observable universe is 93 billion sv. years old.
A visual (in the form of a sphere) representation of the three-dimensional structure of the observed Universe, visible from our position (center of the circle).
White lines the boundaries of the observable Universe are indicated.
Specks of light - these are clusters of clusters of galaxies - superclusters - the largest known structures in space.
Scale bar: one division above is 1 billion light years, below is 1 billion parsecs.
Our house (in the center) here referred to as the Virgo Supercluster, it is a system of tens of thousands of galaxies, including our own Milky Way.
A more visual representation of the scale of the observable Universe is given by the following image:
Layout of the Earth in the Observed Universe - a series of eight maps
from left to right top row: Earth - Solar system - Nearest stars - Milky Way Galaxy, bottom row: Local group of galaxies - Virgo Cluster - Local Supercluster - Observable (observable) Universe.
In order to better feel and understand what colossal, incomparable with our earthly ideas, scales we are talking about, it is worth looking enlarged view of this circuit in media viewer .
What about the entire universe? The size of the entire Universe (Creation, Metaverse), presumably, is much larger!
But, this is what this whole Universe is like and how it is arranged, it still remains a mystery to us ...
What about the center of the universe? The observable Universe has a center - we are! We are at the center of the observable universe, because the observable universe is simply a section of space that is visible to us from Earth.
And just as from a high tower we see a circular area centered in the tower itself, we also see an area of \u200b\u200bspace centered from the observer. In fact, more precisely, each of us is the center of our own observable universe.
But this does not mean that we are in the center of the entire Universe, just like the tower is by no means the center of the world, but only the center of that piece of the world that can be seen from it - to the horizon.
The same is with the observable universe.
When we look into the sky, we see light that has been flying towards us for 13.8 billion years from places that are already 46.5 billion light years away.
We do not see what is beyond this horizon.
Space is called Metagalaxy. It is also called our Universe. This colossal structure consists of a billion, and - only a speck of dust in this set of star systems, the boundaries of which are rapidly. Active research of the Metagalaxy began with the construction of telescopes with a sufficient degree of magnification. With their help, it was possible to look into very distant space. For example, it was found that many light spots are not just, but entire systems of galaxies.
Structure
If we take the average density of the substance of the Metagalaxy, then it will be 10 -31 - 10 -32 g / cm 3. Of course, not all space is the same type, there are large-scale heterogeneities, and there are voids. Some galaxies are grouped into systems. They can be double or more numerous, up to hundreds, thousands and even tens of thousands of galaxies. Such superclusters are called clouds. For example, the Milky Way, and another fifteen hundred galaxies, are included in the local group, which is part of a huge cloud. The central part of this cloud is the nucleus, which consists of a cluster of several thousand galaxies. Prior to this formation, located in the constellations of Coma and Virgo, only 40 million light years. But very little is known about the structure of the Metagalaxy. The same applies to its shape and size. It is only clear that no decrease in the density of distribution of galaxies in any of the directions is found. This testifies to the absence of boundaries of our Universe. Or the area of \u200b\u200bresearch is not large enough. In fact, the structure of the Metagalaxy looks like a honeycomb, and the size of their cells is 100 - 300 million light years. Internal honeycomb cavities - voids - are practically empty, and clusters of galactic clusters are located along the walls.
What are its dimensions
As we found out, the Metagalaxy is the Universe that we are able to survey. It began to expand immediately after its appearance (after the Big Bang). Its boundaries after the explosion are determined by relict radiation, the surface of the last scattering The surface of the last scattering - a distant region of space, on which today's CMB photons were last scattered by ionized matter, now appears from the Earth as a spherical shell. Closer than this surface, the Universe was, in essence, already transparent to radiation. Although the surface has a finite thickness, it is a relatively sharp boundary. is the most distant object of observation.
Outside the boundaries of the Metagalaxy there are objects that have arisen regardless of the results of the Big Bang of our Universe, about which practically nothing is known.
Distances to ultra-long objects
The latest measurements of the most distant object - relic radiation - gave a value of about 14 billion parsecs. Such dimensions were obtained in all directions, from which it follows that the Metagalaxy, most likely, has the shape of a ball. And the diameter of this ball is almost 93 billion light years. If we calculate its volume, then it will be about 11.5 trillion. Mpc 3. But it is known that the Universe itself is much broader than the boundaries of observation. The most distant of the detected galaxies is UDFj-39546284. It is only visible in the infrared range. It is 13.2 billion light years before it, and it appears as it was when the universe was only 480 million years old.
The diameter of the Moon is 3000 km, the Earth is 12800 km, the Sun is 1.4 million kilometers, while the distance from the Sun to the Earth is 150 million km. The diameter of Jupiter, the largest planet in our solar system, is 150,000 km. No wonder they say that Jupiter could be a star, in the video next to Jupiter is located working star, its size () is even smaller than Jupiter. By the way, since you've touched Jupiter, you may not have heard, but Jupiter does not revolve around the Sun. The fact is that the mass of Jupiter is so great that the center of rotation of Jupiter and the Sun is outside the Sun, thus both the Sun and Jupiter revolve together around a common center of rotation.
According to some calculations, there are 400 billion stars in our galaxy, which is called the Milky Way. This is far from the largest galaxy; there are more than a trillion stars in neighboring Andromeda.
As indicated in the video at 4:35 am, our Milky Way will collide with Andromeda in a few billion years. According to some calculations, using any technologies known to us, even improved ones in the future, we will not be able to reach other galaxies, since they are constantly moving away from us. Only teleportation can help us. This is bad news.
The good news is that you and I were born at a good time when scientists see other galaxies and can theorize about the Big Bang and other phenomena. If we were born much later, when all galaxies scattered far from each other, then most likely we would not be able to find out how the universe originated, whether there were other galaxies, whether there was a Big Bang, etc. We would consider that our Milky Way (united by that time with Andromeda) is the only and unique in the whole space. But we are lucky and we know something. Probably.
Let's go back to the numbers. Our small Milky Way contains up to 400 billion stars, neighboring Andromeda is more than a trillion, and there are more than 100 billion such galaxies in the observable universe. And many of them contain several trillion stars. It may seem incredible that there are so many stars in space, but somehow the Americans took and pointed their mighty Hubble telescope at a completely empty space in our sky. After observing him for several days, they got this picture:
In a completely empty area of \u200b\u200bour sky, they found 10 thousand galaxies (not stars), each of which contains billions and trillions of stars. Here is this square in our sky, for scale.
And what is happening outside the observable universe, we do not know. The dimensions of the universe that we see is about 91.5 billion light years. What's next is unknown. Perhaps our entire universe is just a bubble in the seething ocean of the multiverse. In which there may even be other laws of physics, for example, Archimedes' law does not work and the sum of the angles is not equal to 360 degrees.
Enjoy. The dimensions of the universe in the video:
Did you know that the universe we observe has fairly definite boundaries? We are used to associating the Universe with something infinite and incomprehensible. However, modern science to the question of the "infinity" of the Universe offers a completely different answer to such an "obvious" question.
According to modern concepts, the size of the observable universe is approximately 45.7 billion light years (or 14.6 gigaparsecs). But what do these numbers mean?
The first question that comes to mind an ordinary person - how the Universe cannot be infinite at all? It would seem indisputable that the container of everything that exists around us should not have boundaries. If these boundaries exist, what are they?
Let's say some astronaut flew to the borders of the universe. What will he see in front of him? A solid wall? Fire barrier? And what is behind it - emptiness? Another Universe? But can emptiness or another Universe mean that we are on the border of the universe? After all, this does not mean that there is "nothing". Emptiness and another Universe is also "something". But the Universe is something that contains absolutely everything “something”.
We come to an absolute contradiction. It turns out that the border of the Universe should hide from us something that should not be. Or the border of the Universe should fence off “everything” from “something”, but this “something” should also be a part of “everything”. In general, a complete absurdity. Then how can scientists claim the limiting size, mass, and even age of our universe? These values, although unimaginably large, are still finite. Is science arguing with the obvious? To deal with this, let's first trace how humans came to a modern understanding of the universe.
Expanding the boundaries
From time immemorial, man has been interested in what the world around them is. One need not give examples of the three whales and other attempts of the ancients to explain the universe. As a rule, in the end it all came down to the fact that the foundation of all that exists is the earthly firmament. Even in antiquity and the Middle Ages, when astronomers had extensive knowledge of the laws governing the motion of planets along the "stationary" celestial sphere, The Earth remained the center of the universe.
Naturally, back in Ancient Greece there were those who believed that the earth revolved around the sun. There were those who spoke about the many worlds and the infinity of the universe. But constructive justifications for these theories emerged only at the turn of the scientific revolution.
In the 16th century, the Polish astronomer Nicolaus Copernicus made the first major breakthrough in understanding the Universe. He firmly proved that the Earth is only one of the planets orbiting the Sun. Such a system greatly simplified the explanation of such a complex and intricate motion of the planets in the celestial sphere. In the case of a stationary earth, astronomers had to invent all sorts of ingenious theories to explain this behavior of the planets. On the other hand, if the Earth is taken to be mobile, then the explanation for such intricate movements comes naturally. This is how a new paradigm called "heliocentrism" was established in astronomy.
Many Suns
However, even after that, astronomers continued to confine the universe to the "sphere of fixed stars." Until the 19th century, they could not estimate the distance to the stars. For several centuries, astronomers have tried unsuccessfully to detect deviations in the position of stars relative to the Earth's orbital motion (annual parallaxes). The instruments of those times did not allow such accurate measurements.
Finally, in 1837, the Russian-German astronomer Vasily Struve measured the parallax. This marked a new step in understanding the scale of space. Now scientists could safely say that stars are distant similarities to the Sun. And our luminary from now on is not the center of everything, but an equal "inhabitant" of the endless star cluster.
Astronomers have come even closer to understanding the scale of the universe, because the distances to the stars turned out to be truly monstrous. Even the size of the orbits of the planets seemed insignificant compared to this. Then it was necessary to understand how the stars are concentrated in.
Many Milky Way
The famous philosopher Immanuel Kant anticipated the foundations of the modern understanding of the large-scale structure of the Universe back in 1755. He hypothesized that the Milky Way is a huge rotating cluster of stars. In turn, many of the observed nebulae are also more distant "milky ways" - galaxies. Despite this, until the 20th century, astronomers adhered to the fact that all nebulae are sources of star formation and are part of Milky way.
The situation changed when astronomers learned to measure distances between galaxies using. The absolute luminosity of stars of this type is strictly dependent on the period of their variability. Comparing their absolute luminosity with the visible one, it is possible to determine the distance to them with high accuracy. This method was developed in the early 20th century by Einar Herzsrung and Harlow Shelpy. Thanks to him, the Soviet astronomer Ernst Epik in 1922 determined the distance to Andromeda, which turned out to be an order of magnitude larger than the size of the Milky Way.
Edwin Hubble continued Epic's endeavor. By measuring the brightness of Cepheids in other galaxies, he measured the distance to them and compared it with the redshift in their spectra. So in 1929 he developed his famous law. His work has definitively refuted the established belief that the Milky Way is the edge of the universe. Now he was one of the many galaxies that once believed him part of... Kant's hypothesis was confirmed almost two centuries after its development.
Subsequently, the connection between the distance of the galaxy from the observer and the speed of its removal from the observer, discovered by Hubble, made it possible to compose a complete picture of the large-scale structure of the Universe. It turned out that galaxies were only a tiny part of it. They linked into clusters, clusters into superclusters. In turn, superclusters fold into the largest known structures in the universe - filaments and walls. These structures, adjacent to huge supervoids (), make up the large-scale structure of the currently known Universe.
Apparent infinity
From the foregoing, it follows that in just a few centuries, science has gradually leapt from geocentrism to a modern understanding of the Universe. However, this does not answer why we are limiting the universe these days. After all, until now, it was only about the scale of the cosmos, and not about its very nature.
The first who decided to justify the infinity of the Universe was Isaac Newton. Opening the law universal gravitation, he believed that if space was finite, all her bodies would sooner or later merge into a single whole. Before him, if someone expressed the idea of \u200b\u200bthe infinity of the Universe, it was exclusively in a philosophical key. Without any scientific justification. An example of this is Giordano Bruno. By the way, like Kant, he was ahead of science by many centuries. He was the first to declare that the stars are distant suns, and planets revolve around them too.
It would seem that the very fact of infinity is quite justified and obvious, but the turning points of science of the 20th century shook this "truth".
Stationary universe
The first significant step towards the development of a modern model of the universe was made by Albert Einstein. The famous physicist introduced his model of a stationary universe in 1917. This model was based on the general theory of relativity, which he developed the same year earlier. According to his model, the universe is infinite in time and finite in space. But after all, as noted earlier, according to Newton, a universe with a finite size must collapse. To do this, Einstein introduced a cosmological constant, which compensated for the gravitational attraction of distant objects.
As paradoxical as it may sound, Einstein did not limit the very finiteness of the universe. In his opinion, the Universe is a closed shell of a hypersphere. An analogy is the surface of an ordinary three-dimensional sphere, for example, a globe or the Earth. No matter how much a traveler travels around the Earth, he will never reach its edge. However, this does not mean that the Earth is infinite. The traveler will simply return to the place where he started his journey.
On the surface of the hypersphere
Likewise, a space wanderer, overcoming Einstein's universe on a starship, can return back to Earth. Only this time the wanderer will move not along the two-dimensional surface of the sphere, but along the three-dimensional surface of the hypersphere. This means that the Universe has a finite volume, and hence a finite number of stars and mass. However, the Universe has no boundaries or any center.
Einstein came to such conclusions by linking space, time and gravity in his famous theory. Before him, these concepts were considered separate, which is why the space of the Universe was purely Euclidean. Einstein proved that gravity itself is a curvature of spacetime. This radically changed the early ideas about the nature of the Universe, based on classical Newtonian mechanics and Euclidean geometry.
Expanding Universe
Even the discoverer himself " new universe"Was no stranger to delusions. Although Einstein limited the universe in space, he continued to consider it static. According to his model, the Universe was and remains eternal, and its size always remains the same. In 1922, Soviet physicist Alexander Fridman significantly expanded this model. According to his calculations, the universe is not at all static. It can expand or contract over time. It is noteworthy that Friedman came to such a model, based on the same theory of relativity. He was able to more correctly apply this theory, bypassing the cosmological constant.
Albert Einstein did not immediately accept this "amendment". The Hubble discovery mentioned earlier came to the rescue of this new model. The scattering of galaxies indisputably proved the fact of the expansion of the Universe. So Einstein had to admit his mistake. Now the universe had a certain age, which strictly depends on the Hubble constant, which characterizes the rate of its expansion.
Further development of cosmology
As scientists tried to solve this issue, many other important components of the universe were discovered and various models were developed. So in 1948, Georgy Gamow introduced the hypothesis "about a hot Universe", which would later turn into the big bang theory. The discovery in 1965 confirmed his guesses. Astronomers could now observe the light that came from the moment the universe became transparent.
Dark matter, predicted in 1932 by Fritz Zwicky, was confirmed in 1975. Dark matter actually explains the very existence of galaxies, galaxy clusters, and the Universe itself as a whole. So scientists learned that most of the mass of the Universe is completely invisible.
Finally, in 1998, during a study of the distance to, it was discovered that the universe is expanding with acceleration. This next turning point in science gave rise to the modern understanding of the nature of the universe. The cosmological coefficient, introduced by Einstein and refuted by Friedman, has again found its place in the model of the Universe. The presence of the cosmological coefficient (cosmological constant) explains its accelerated expansion. To explain the presence of a cosmological constant, the concept was introduced - a hypothetical field containing most of the mass of the Universe.
Current understanding of the size of the observable universe
The current model of the universe is also called the ΛCDM model. The letter "Λ" denotes the presence of a cosmological constant that explains the accelerated expansion of the universe. CDM means the universe is filled with cold dark matter. Recent studies indicate that the Hubble constant is about 71 (km / s) / Mpc, which corresponds to the age of the Universe 13.75 billion years. Knowing the age of the universe, one can estimate the size of its observable region.
According to the theory of relativity, information about any object cannot reach the observer with a speed greater than the speed of light (299792458 m / s). It turns out that the observer sees not just an object, but its past. The further the object is from it, the more distant past it looks. For example, looking at the Moon, we see what it was a little over a second ago, the Sun more than eight minutes ago, the nearest stars - years, galaxies - millions of years ago, etc. In Einstein's stationary model, the Universe has no age limit, which means that its observable region is also not limited by anything. The observer, armed with more and more advanced astronomical instruments, will observe more and more distant and ancient objects.
We have a different picture with modern model The universe. According to her, the Universe has an age, and therefore a limit of observation. That is, since the birth of the Universe, no photon would have had time to travel a distance greater than 13.75 billion light years. It turns out that we can state that the observable Universe is limited from the observer by a spherical region with a radius of 13.75 billion light years. However, this is not quite true. Do not forget about the expansion of the space of the Universe. Until the photon reaches the observer, the object that emitted it will be 45.7 billion sv from us. years old. This size is the horizon of particles, and it is the boundary of the observable universe.
Over the horizon
So, the size of the observable Universe is divided into two types. Visible size, also called the Hubble radius (13.75 billion light years). And the real size, called the particle horizon (45.7 billion light years). Essentially, both of these horizons do not at all characterize the real size of the Universe. First, they depend on the position of the observer in space. Second, they change over time. In the case of the ΛCDM model, the particle horizon expands at a speed greater than the Hubble horizon. The question of whether this trend will change in the future, modern science does not give an answer. But if we assume that the Universe continues to expand with acceleration, then all those objects that we see now, sooner or later, will disappear from our "field of view."
At the moment, the most distant light observed by astronomers is the microwave background radiation. Looking into it, scientists see the Universe as it was 380 thousand years after the Big Bang. At this moment, the Universe has cooled so much that it was able to emit free photons, which are captured today with the help of radio telescopes. In those days, there were no stars or galaxies in the Universe, but only a solid cloud of hydrogen, helium and an insignificant amount of other elements. From the inhomogeneities observed in this cloud, galactic clusters will subsequently form. It turns out that exactly those objects that are formed from the inhomogeneities of the relict radiation are located closest to the particle horizon.
True boundaries
Whether the universe has true, unobservable boundaries is still the subject of pseudoscientific conjectures. One way or another, everyone converges at the infinity of the Universe, but they interpret this infinity in completely different ways. Some consider the Universe to be multidimensional, where our “local” three-dimensional Universe is just one of its layers. Others say that the universe is fractal - which means that our local universe may be a particle of another. Do not forget about the various models of the Multiverse with its closed, open, parallel Universes, wormholes. And there are many, many different versions, the number of which is limited only by human imagination.
But if we turn on cold realism or simply move away from all these hypotheses, then we can assume that our Universe is an infinite homogeneous repository of all stars and galaxies. Moreover, at any very distant point, be it billions of gigaparsecs away from us, all conditions will be exactly the same. At this point, there will be exactly the same horizon of particles and the Hubble sphere with the same relic radiation at their edge. There will be the same stars and galaxies around. Interestingly, this does not contradict the expansion of the universe. After all, it is not just the Universe that is expanding, but its very space. The fact that at the moment of the big bang the Universe arose from one point only says that the infinitely small (practically zero) dimensions that were then have now turned into unimaginably large. In the future, we will use this particular hypothesis in order to clearly understand the scale of the observed Universe.
Visual representation
Various sources provide all kinds of visual models that allow people to understand the scale of the universe. However, it is not enough for us to realize how big the cosmos is. It is important to understand how concepts such as the Hubble horizon and the particle horizon actually manifest. To do this, let's imagine our model step by step.
Let's forget that modern science does not know about the "foreign" region of the Universe. Discarding the versions about the multiverse, the fractal Universe and its other "varieties", imagine that it is simply infinite. As noted earlier, this does not contradict the expansion of her space. Of course, let's take into account the fact that its Hubble sphere and the sphere of particles are respectively equal to 13.75 and 45.7 billion light years.
The scale of the universe
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To begin with, let's try to realize how large the universal scale is. If you have traveled around our planet, then you can well imagine how big the Earth is for us. Now let's imagine our planet as a buckwheat grain that orbits around a watermelon-Sun half the size of a football field. In this case, the orbit of Neptune will correspond to the size of a small city, the area to the Moon, the area of \u200b\u200bthe Sun's influence boundary to Mars. It turns out that our Solar System is as much larger than the Earth as Mars is larger than buckwheat! But this is just the beginning.
Now let's imagine that this buckwheat will be our system, the size of which is approximately equal to one parsec. Then the Milky Way will be the size of two football stadiums. However, even this will not be enough for us. We'll have to reduce the Milky Way to a centimeter size. It will in some way resemble coffee foam wrapped in a whirlpool in the middle of the coffee-black intergalactic space. Twenty centimeters from it there is the same spiral "crumb" - the Andromeda Nebula. Around them will be a swarm of small galaxies from our Local Cluster. The apparent size of our Universe will be 9.2 kilometers. We have come to an understanding of the Universal dimensions.
Inside the universal bubble
However, it is not enough for us to understand the scale itself. It is important to understand the dynamics of the universe. Let's imagine ourselves as giants for which the Milky Way has a centimeter diameter. As noted just now, we will find ourselves inside a sphere with a radius of 4.57 and a diameter of 9.24 kilometers. Let's imagine that we are able to hover inside this sphere, travel, overcoming entire megaparsecs in a second. What will we see if our Universe is infinite?
Of course, before us there will be an infinite number of all kinds of galaxies. Elliptical, spiral, irregular. Some areas will be teeming with them, others will be empty. The main feature will be that visually they will all be motionless while we are motionless. But as soon as we take a step, the galaxies themselves will begin to move. For example, if we are able to see in the centimeter Milky Way a microscopic Solar System, then we can observe its development. Moving 600 meters away from our galaxy, we will see the protostar Sun and the protoplanetary disk at the time of formation. Approaching it, we will see how the Earth appears, life arises and man appears. Likewise, we will see how galaxies change and move as we move away or approach them.
Consequently, than in more distant galaxies we will peer, the more ancient they will be for us. So the most distant galaxies will be located further than 1300 meters from us, and at the turn of 1380 meters we will see the relic radiation. True, this distance will be imaginary for us. However, as we get closer to the relic radiation, we will see an interesting picture. Naturally, we will observe how galaxies will form and develop from the original cloud of hydrogen. When we reach one of these formed galaxies, we will understand that we have overcome not 1.375 kilometers at all, but all 4.57.
Downsizing
As a result, we will increase even more in size. Now we can place whole voids and walls in the fist. So we find ourselves in a rather small bubble, from which it is impossible to get out. Not only will the distance to objects at the edge of the bubble increase as they get closer, but the edge itself will drift infinitely. This is the whole point of the size of the observable universe.
No matter how big the Universe is, for the observer it will always remain a limited bubble. The observer will always be in the center of this bubble, in fact, he is its center. Trying to get to any object at the edge of the bubble, the observer will shift its center. As it approaches the object, this object will move further and further from the edge of the bubble and at the same time will change. For example, from a shapeless hydrogen cloud it will turn into a full-fledged galaxy or further into a galaxy cluster. In addition, the path to this object will increase as you approach it, as the surrounding space itself will change. Once we get to this object, we just move it from the edge of the bubble to its center. At the edge of the universe, the relic radiation will also flicker.
If we assume that the Universe will continue to expand at an accelerated rate, then being in the center of the bubble and winding time for billions, trillions and even higher orders of years in advance, we will notice an even more interesting picture. Although our bubble will also grow in size, its mutating components will move away from us even faster, leaving the edge of this bubble, until each particle of the Universe wanders scattered around in its lonely bubble without the ability to interact with other particles.
So, modern science does not have information about what the real dimensions of the Universe are and whether it has boundaries. But we know for sure that the observable Universe has a visible and true boundary, called the Hubble radius (13.75 billion light years) and the radius of particles (45.7 billion light years), respectively. These boundaries are completely dependent on the position of the observer in space and expand over time. If the Hubble radius expands strictly at the speed of light, then the expansion of the particle horizon is accelerated. The question of whether its acceleration of the particle horizon will continue further and whether it will not change to compression remains open.
You probably think the universe is infinite? May be so. It is unlikely that we will ever know about this for sure. It will not work to cover our entire universe with a glance. Firstly, this fact follows from the concept of the "big bang", which claims that the universe has its own, so to speak, birthday, and, secondly, from the postulate that the speed of light is a fundamental constant. So far, the observable portion of the universe, which is 13.8 billion years old, has expanded in all directions by 46.1 billion light years. The question arises: what was the size of the universe then, 13.8 billion years ago? This question was asked by someone Joe Muscarella. Here's what he writes:
“I have seen different answers to the question of what was the size of our universe shortly after the end of the period of cosmic inflation (cosmic inflation - the phase preceding the Big Bang - approx. Transl.). In one source it is indicated - 0.77 centimeters, in another - the size of a soccer ball, and in the third - larger than the size of the observed universe. So which one? Or maybe some kind of intermediate one? "
Context
The big bang and the "black hole"
Die Welt 02/27/2015How the Universe Created Man
Nautilus 01/27/2015 By the way, the past year just gives us a reason to talk about Einstein and the essence of space-time, because last year we celebrated the centenary of the general theory of relativity. So let's talk about the universe.When we observe distant galaxies through a telescope, we can determine some of their parameters, for example, the following:
- redshift (i.e. how much the light emitted by them has shifted with respect to the inertial frame of reference);
- object brightness (i.e. measure the amount of light emitted by a distant object);
Is the corner radius of the object.
These parameters are very important, because if we know the speed of light (one of the few parameters that we know), as well as the brightness and size of the observed object (we also know these parameters), then we can determine the distance to the object itself.
In fact, one has to be content with only approximate characteristics of the brightness of the object and its dimensions. If an astronomer observes a supernova explosion in some distant galaxy, then the corresponding parameters of other supernovae located in the vicinity are used to measure its brightness; we assume that the conditions in which these supernovae erupted are similar, and there is no interference between the observer and the space object. Astronomers distinguish the following three types of factors that determine the observation of a star: stellar evolution (the difference between objects depending on their age and distance), an exogenous factor (if the real coordinates of the observed objects differ significantly from the hypothetical ones) and the interference factor (if, for example, the transmission of light are influenced by interference, such as dust) - and this is all, among other factors, unknown to us.
By measuring the brightness (or size) of the observed object, using the ratio "brightness / distance", you can determine the distance of the object from the observer. Moreover, according to the characteristics of the object's redshift, one can determine the scale of the expansion of the universe during the time during which the light from the object reaches the Earth. Using the relationship between matter-energy and space-time, about which Einstein's general theory of relativity speaks, it is possible to consider all kinds of combinations of various forms of matter and energy available at the moment in the universe.
But that is not all!
If you know what parts the universe consists of, then using extrapolation, you can determine its size, as well as learn about what happened at any stage in the evolution of the universe, and what was the energy density at that time. As you know, the universe consists of the following components:
- 0.01% - radiation (photons);
- 0.1% - neutrinos (heavier than photons, but a million times lighter than electrons);
- 4.9% - common matter, including planets, stars, galaxies, gas, dust, plasma and black holes;
- 27% - dark matter, i.e. its kind that participates in the gravitational interaction, but differs from all particles of the Standard Model;
- 68% - dark energy, causing the expansion of the universe.
As you can see, dark energy is an important thing, it was discovered quite recently. For the first nine billion years of its history, the universe consisted mainly of matter (in the form of a combination of ordinary matter and dark matter). However, for the first few millennia, radiation (in the form of photons and neutrinos) was an even more important building material than matter!
Note that each of these constituent parts of the universe (i.e. radiation, matter, and dark energy) affect the rate of its expansion differently. Even if we know that the universe is 46.1 billion light-years long, we must know the exact combination of its constituent elements at each stage of its evolution in order to calculate the size of the universe at any time in the past.
- when the universe was about three years old, the diameter of the Milky Way was one hundred thousand light years;
- when the universe was one year old, it was much hotter and denser than it is now; the average temperature exceeded two million degrees Kelvin;
- one second after its birth, the universe was too hot for stable nuclei to form in it; at that moment protons and neutrons were floating in a sea of \u200b\u200bhot plasma. In addition, at that time, the radius of the universe (if we take the Sun as the center of the circle) was such that only seven of all currently existing star systems closest to us could fit into the described circle, the most distant of which would be Ross 154 (Ross 154 - a star in the constellation Sagittarius, a distance of 9.69 light years from the Sun - approx. Lane);
- when the age of the universe was only one trillionth of a second, its radius did not exceed the distance from the Earth to the Sun; in that era, the expansion rate of the universe was 1029 times greater than it is now.
If you wish, you can see what happened at the final stage of inflation, i.e. just before the Big Bang. The singularity hypothesis could be used to describe the state of the universe at the earliest stage of its birth, but thanks to the inflation hypothesis, there is no need for a singularity. Instead of a singularity, we are talking about a very rapid expansion of the universe (i.e. inflation) that took place over a period of time before the hot and dense expansion that started the current universe. Now let's move on to the final stage inflation of the universe (time interval between 10 minus 30 - 10 minus 35 seconds). Let's see what the size of the universe was at the moment when inflation stopped and the big bang occurred.
Here we are talking about the observable part of the universe. Its true size is certainly much larger, but we don't know how much. In the best possible approximation (judging by the data contained in the Sloan Digital Sky Survey (SDSS) and information received from the Planck Space Observatory), if the universe is curved and collapsed, then its observable part is so indistinguishable from the "undistorted" that the entire its radius should be at least 250 times the radius of the observed part.
In truth, the extent of the universe may even be infinite, since the way it behaved on early stage inflation, we do not know except for the last fractions of a second. But if we talk about what happened during inflation in the observable part of the universe at the very last moment (in the interval between 10 at minus 30 and 10 at minus 35 seconds) before the Big Bang, then we know the size of the universe here: it varies between 17 centimeters (at 10 in minus 35 seconds) and 168 meters (at 10 in minus 30 seconds).
What is seventeen centimeters? It's almost the diameter of a soccer ball. So, if you want to know which of the indicated dimensions of the universe is closest to the real one, then stick to this figure. And if we assume the size is less than a centimeter? This is too little; however, given the limitations imposed by cosmic microwave radiation, it turns out that the expansion of the universe could not have ended with such high level energies, and hence the above-mentioned size of the universe at the very beginning of the "Big Bang" (ie, the size not exceeding a centimeter) is excluded. If the size of the universe exceeded the current one, then in this case it makes sense to talk about the existence of an unobservable part of it (which is probably correct), but we have no way to measure this part.
So what was the size of the universe at the time of its inception? If you believe the most authoritative mathematical models describing the stage of inflation, then it turns out that the size of the universe at the time of its inception will fluctuate somewhere between the size of a human head and a city block built up with skyscrapers. And there, you see, only some 13.8 billion years will pass - and the universe in which we live appeared.